Total pennant loot is about 30% capped by around 520 with adjustments for age difference and power level difference.

You are going to attack a Saracens with 4000 , 2000 , 1000 pennants. In this case, 511 pennants are available and you loot all of them. Then you will gain 511 . The Saracens player will lose 511 pennants, but not all Saracens - they'll be lost according to the share of total pennants!